This application pertains to low shrink molding resin systems and relates to commonly assigned and allowed application identified as Ser. No. 330,474 filed Feb. 8, 1973, now U.S. Pat. No. 3,883,612, issued May 13, 1975 and said application is incorporated herein by reference.
Unsaturated polyester polymers blended with vinyl monomers such as styrene are well-known molding resins that can be cured at room temperature or under heat and/or pressure to form a thermoset plastic molded part. These molding resins often are combined with inert fillers, glass fibers, glass flakes, talcs, and the like for the purpose of obtaining improved impact strength, flexural strength, and rigidity in molded parts. Most conventional thermosetting resins, however, characteristically shrink about 8% to 10% by volume and consequently distort during the molding process whereby the shrinkage thereof is unsatisfactory despite the many favorable inherent characteristics of polyester molding compositions. To offset the shrinkage characteristic, resin systems have been suggested based primarily on a resin system of a thermosetting polyester polymer, a thermoplastic addition polymer, and a reactive ethylenically unsaturated monomer.
A particularly desirable low shrink resin composition is a stabilized one-component system disclosed in Ser. No. 330,474 filed Feb. 8, 1973, and copending herewith which provides a dicyclopentadiene-modified polyester resin intermixed primarily with a modified acrylic thermoplastic polymer having acid functionality.
It now has been found that an improved low shrink thermosetting polyester resin system can be achieved by dispersing a thermoplastic, branched, fatty acid modified alkyd dispersed within a dicyclopentadiene-modified polyester resin to produce a stabilized, uniform dispersion mixture.